The present invention generally relates to semiconductor integrated circuit technology and, more particularly, to techniques for employing a reactive pad in contact with the surface of a workpiece during material removal or planarization.
Removal of excess material in a uniform manner from the surface of coated patterned substrates has wide range of applications. One of these applications is in the field of integrated circuit manufacturing. Conventional semiconductor devices such as integrated circuits generally include a semiconductor substrate, usually a silicon substrate, and a plurality of sequentially formed dielectric interlayers such as silicon dioxide, and conductive paths or interconnects made of conductive materials. Copper and copper alloys have recently received considerable attention as interconnect materials because of their superior electromigration and low resistivity characteristics. The interconnects are usually formed by filling a conductor such as copper in features or cavities etched into the dielectric interlayers by a metallization process. In an integrated circuit, multiple levels of interconnect networks laterally extend with respect to the substrate surface. Interconnects formed in sequential layers can be electrically connected using features such as vias or contacts.
In a typical interconnect fabrication process, first an insulating interlayer is formed on the semiconductor substrate. Patterning and etching processes are performed to form features such as trenches, pads and vias etc. in the insulating layer. Then, copper is deposited on the substrate through a metallization process to fill all the features. The preferred method of copper metallization process is electroplating.
FIG. 1 illustrates a cross-sectional view of a substrate 102 such as a wafer with features 104 such as trenches and vias formed into its insulating layer. A material 106, such as copper (Cu) is deposited on the wafer 102 surface over the features 104. In conventional deposition processes, a barrier layer 108, and then, in the case of copper 106 deposition, a very thin copper seed layer to initiate copper growth, are coated onto the insulating layer and into the features of the insulating layer of the wafer 102. The goal of a planarization process is to remove the material 106 from the top surface of the wafer 102, leaving the material 106 only in the features 104. This is presently achieved by a polishing technique such as chemical mechanical polishing (CMP), electropolishing, etching, or a combination of these techniques. The polishing techniques are conducted to remove the excess material 106 layer or material overburden and other conductive layers that are above the top surface of the insulating portions of substrate 102. FIG. 2 shows the cross-section of the same substrate 102 after the polishing technique(s) are applied and the excess conductors are removed. The substrate is planarized so that the material 106 is only in the features 104.
In most commonly used CMP approaches, the substrate 102 surface is contacted with a pad and the pad is moved with respect to the substrate surface. This pad is typically made of a polymeric material which is inert to the material 106. The pad may or may not contain abrasive particles or gels. The hardness of the pad may change in accordance with the material to be removed. Companies such as 3M, Rodel, and Universal Photonics supply CMP pads of various types to the industry. The role of the pad is to polish the surface of the substrate 102 and to remove the material 106 on the surface with the help of, for example, a chemical solution or a slurry containing abrasive particles. Therefore, slurry apart, the role of the pad in prior processes is purely mechanical. Conventionally, chemical reactions occur between the film to be removed and the slurry. The reaction products are then removed by the pad and the abrasive particles.
There are many challenges with the state-of-the art CMP techniques. These include but are not limited to: the pads getting glazed and loosing their efficiency, the stability of the removal rate from run to run, the cost of the consumables, and the defects such as dishing and erosion which are well known and characterized by those skilled in the art and in the field.
The higher the pressure, the higher the metal removal rates during CMP operations. Higher polishing pressures of, for example, three to six pounds per square inch (psi), while practical for strong dielectric films such as silicon dioxide, are problematic for many films with low dielectric constants, such as SOX, SILK, diamond like carbon (DLC), and their likes. This is because they tend to be more fragile than silicon dioxide. In general, CMP operations that occur at low pressures, for example, less than three psi, result in lower metal removal rates, hence lower process throughput and higher operating costs.
To this end, it would be desirable to have a more efficient method and system for providing material removal and planarization of the surface of a substrate such as a semiconductor wafer surface.
The presently preferred embodiments described herein include systems and methods for providing material removal and planarization of the surface of a workpiece such as, for example, a semiconductor device or wafer, a packaging substrate, or a magnetic device, using a reactive pad.
A method of removing a first material located on a top surface of a workpiece using a pad positioned proximate to the workpiece is presented according to one aspect of the present invention. The pad is positioned proximate to the workpiece so that a front surface of the pad contacts an exposed surface of the first material. The pad includes a second material. The front surface of the pad is mechanically moved against the exposed surface of the first material to initiate a chemical reaction between the first material and the second material. The chemical reaction yields a reaction product. The reaction product is removed using a chemical solution. The reaction product is soluble into the chemical solution and the first material and second material are not substantially soluble into the chemical solution.
A method of removing a first material located on a top surface of a workpiece using a pad positioned proximate to the workpiece is presented according to another aspect of the present invention. The pad is positioned proximate to the workpiece so that a front surface of the pad contacts an exposed surface of the first material. The pad includes a second material. The front surface of the pad is mechanically moved against the exposed surface of the first material to initiate a chemical reaction between the first material and the second material. The chemical reaction yields a reaction product. The reaction product is removed using the mechanical movement of the front surface of the pad against the exposed surface of the first material. The mechanical movement is not sufficient to remove the first material but is sufficient to remove the reaction product.
A method of removing a first material located on a top surface of a workpiece using a pad positioned proximate to the workpiece is presented according to a further aspect of the present invention. The pad is positioned proximate to the workpiece so that a front surface of the pad contacts an exposed surface of the first material. The pad includes a second material. The front surface of the pad is mechanically moved against the exposed surface of the first material to initiate a chemical reaction between the first material and the second material. The chemical reaction yields a reaction product. The reaction product is removed using a chemical solution and the mechanical movement of the front surface of the pad against the exposed surface of the first material. The reaction product is soluble into the chemical solution and the first material and second material are not substantially soluble into the chemical solution. The mechanical movement is not sufficient to remove the first material but is sufficient to remove the reaction product.
A method of removing a material on a surface of a workpiece using a reactive pad positioned in very close proximity to the workpiece is presented according to another aspect of the present invention. The pad is sufficiently close to the workpiece, while not touching the workpiece during the material removal process. The reactive pad and workpiece may vibrate and or move mechanically with respect to each other during the materials removal process and the removal rate is independent of the applied pressure.
A method of removing a material from a surface of a workpiece using a reactive pad positioned sufficiently near to the workpiece, such that the reactive pad barely touches the surface of the material to be removed, and so that the reactive pad is subjected to near zero deformation or non-significant deformation with respect to its thickness, is presented according to a further aspect of the present invention. The reactive pad and the workpiece may vibrate or move mechanically with respect to each other during the material removal process.
A method of removing a material from a surface of a workpiece using a combination pad, is presented according to another aspect of the present invention. The combination pad material is a combination of a reactive pad and a conventional mechanical pad, such that some portions of the combination pad material include a reactive pad material and other portions of the combination pad material include conventional mechanical pad material. During the material planarization process, the workpiece is positioned very close to the pad so as to be in contact with the combination pad material. Both the workpiece and the combination pad material move with respect to each other.
A method and arrangement of removing a material from a surface of a workpiece using a combination of a reactive pad and a mechanical pad, such that the reactive pad is positioned adjacent to a mechanical pad, is presented according to a further aspect of the present invention. During planarization of the workpiece, the workpiece may vibrate or move mechanically with respect to the pad. Some portions of the material on the workpiece are removed using the reactive pad, while other portions of the material are removed using the mechanical pad.